A network processor generally controls the flow of packets between a physical transmission medium, such as a physical layer portion of, e.g., an asynchronous transfer mode (ATM) network or synchronous optical network (SONET), and a switch fabric in a router or other type of packet switch. Such routers and switches generally include multiple network processors, e.g., arranged in the form of an array of line or port cards with one or more of the processors associated with each of the cards.
In performing packet processing operations such as routing or switching, the network processor typically must examine at least a portion of the beginning or head of each packet. The amount of each packet that must be examined is dependent upon its associated network communication protocols, enabled options, and other similar factors. The sophistication or complexity of the router or switch can also influence the amount of each packet that will need examination.
Many conventional routers and switches are configured to store, for a given packet being processed, substantially the entire packet, until that packet is finally transmitted to its destination or dropped. The packet is usually stored in a router or switch memory external to the associated network processor. The amount of time the given packet may be kept in external memory is influenced by the basic processing time of the router or switch, the quality of service applied to the packet, the particular protocol layers to be analyzed, and the congestion of the port or other communication channel to which the packet is directed.
High-speed routers and switches will typically store in on-chip memory within the network processor some portion of a given packet being processed by that network processor. This greatly enhances the performance of the router or switch by not requiring it to access the larger external memory holding the entire packet, in that the external memory is slower and more band-limited than the on-chip memory. However, in conventional practice, the worst-case packet portion that may need to be analyzed in a given router or switch application usually dictates the size of every packet portion kept in on-chip memory, even though the worst-case packet portion may be associated with only certain rarely-occurring packets. This significantly increases the required size of the on-chip memory, and thus the cost and complexity of the network processor.
It is therefore apparent that a need exists for improved techniques for determining particular portions of packets to be stored in particular memories associated with a network processor or other type of processor, so as to reduce the memory requirements of the device.